Someone who thinks they're cool when they're not, and would do something lame and noob-ish like smoking weed off a can when really, joint paper costs, like, 2 bucks, and it doesn't make you look like a huge douchefruit (see 'douchefruit' definition). Cansmoker is not a term completely exclusive to marijuana, however, and can be used to describe anyone ameteur and douchey.

Elsa called me a cansmoker just because she caught me shaving my arms.